Group III nitride compound semiconductor device

ABSTRACT

An undercoat layer inclusive of a metal nitride layer is formed on a substrate. Group III nitride compound semiconductor layers are formed on the undercoat layer continuously.

This is a Divisional of U.S. application Ser. No. 09/518,724, filed Mar.3, 2000 now U.S. Pat. No. 6,426,512 the entire contents of which areincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a group III nitride compound semiconductordevice. More particularly, it relates to an improvement in an undercoatlayer for a group III nitride compound semiconductor layer such as a GaNsemiconductor layer.

The present application is based on Japanese Patent Applications No.Hei. 11-58128, 11-60206, 11-611155, 11-90833, and 11-235450, which areincorporated herein by reference.

2. Description of the Related Art

The fact that a (111) face of metal nitride exhibiting an NaCl structureas an undercoat layer is used as a substrate to obtain a group IIInitride compound semiconductor layer, such as a GaN semiconductor layer,of a good crystal has been disclosed in Japanese Patent Publication No.Hei. 9-237938. That is, in Japanese Patent Publication No. Hei.9-237938, metal nitride exhibiting an NaCl structure is used as asubstrate so that a group III nitride compound semiconductor layer isgrown on a (111) face of the substrate.

A substrate for a semiconductor device needs certain characteristicssuch as stiffness, impact resistance, etc. for keeping to maintain thefunction of the device. It is thought that the substrate needs athickness of 100 μm or larger in order to keep the characteristic whenthe substrate is formed of metal nitride.

Metal nitride having such a thickness, however, has not been provided asa raw material of an industrial product used for production of asemiconductor.

Therefore, when an invention described in Japanese Patent PublicationNo. Hei. 9-237938 is to be carried out, the substrate of metal nitridemust be produced personally (probably by a sputtering, or the like) witha great deal of labor.

Incidentally, it is known that, among group III nitride compoundsemiconductors, a GaN semiconductor can be used for a bluelight-emitting device. In such a light-emitting device, sapphire isgenerally used as a substrate.

One of the problems to be solved in the sapphire substrate is asfollows. That is, the sapphire substrate is transparent, so that lightof the light emitting device to be originally taken out from an upperface of the device passes through the sapphire substrate. Hence, lightemitted from the light-emitting device cannot be used effectively.

Moreover, the sapphire substrate is expensive.

Moreover, the sapphire substrate is an electrical insulator, so that itis necessary to form electrodes on one face side. Hence, thesemiconductor layer must be etched partially, so that a bonding processtwice as long is required correspondingly. Further, because n-type andp-type electrodes are formed on one face side, reduction of the devicesize is limited. In addition, there is a “charge-up” problem.

On the other hand, substituting an Si (silicon) substrate for thesapphire substrate may be thought of. According to the inventors'examination, it was, however, very difficult to grow a GaN semiconductorlayer on the Si substrate. On cause of the difficulty is the differencein thermal expansibility between Si and the GaN semiconductor. Thelinear expansion coefficient of Si is 4.7×10⁻⁶/K whereas the linearexpansion coefficient of GaN is 5.59×10⁻⁶/K. The former is smaller thanthe latter. Accordingly, if heating is performed when the GaNsemiconductor layer is grown, the device is deformed so that the Sisubstrate is expanded while the GaN semiconductor layer side iscontracted relatively. On this occasion, tensile stress is generated inthe GaN semiconductor layer, so that there is a risk of occurrence ofcracking as a result. Even in the case where cracking does not occur,distortion occurs in the lattice. Hence, the GaN semiconductor devicecannot fulfill its original function.

FIG. 26 shows an example of a group III nitride compound semiconductordevice with a group III metal nitride semiconductor layer grown on asapphire substrate. In a semiconductor device 1, all of a p-type layer 6and a light-emitting layer 5 and part of an n-type layer 4 are removedby means of etching. Further, an n-type electrode 9 is connected to arevealed portion of the n-type layer 4. Incidentally, in FIG. 26, thereference numerals 2, 3, 7 and 8 designate a substrate, a buffer layer,a light-transmissible electrode and a p-type electrode respectively.

The inventors have examined the light-emitting device configured asdescribed above. As a result, problems to be solved have been found asfollows.

The thickness of the substrate 2 is about 100 μm, and the thickness ofeach of layers 3 to 7 is about 5 μm. On the contrary, size of thelateral direction of the semiconductor device 1 is about 350 μm. Whenthe LED is put on the light, the current must be flowed in the lateraldirection of the n-type layer 4. As a result, the distance of theelectricity path increases and resistance is increased unavoidably.Further, the thickness of an n-type layer portion 4A touching thelight-emitting layer 5 is different from the thickness of an n-typelayer portion 4B which forms an n-electrode 9. Hence, currentconcentration occurs in the boundary between the thick portion 4A andthe thin portion 4B. As a result, the operating voltage of the devicebecomes high. There is also a problem that withstand electrostaticstress characteristic is worsened because of the current concentration.Moreover, when the aforementioned configuration is applied to a generalelectronic device such as a rectifier, a thyristor, a transistor, anFET, or the like, the operating voltage of the device becomes high.Hence, there is a further problem that the permissible current cannot beset to be large.

SUMMARY OF THE INVENTION

An object of the present invention is to form a group III nitridecompound semiconductor layer, especially, a GaN semiconductor layer, ofa good crystal structure by using industrially available raw materials.As a result, a semiconductor device according to the present inventioncan be provided with a semiconductor layer of a good crystal structureand produced inexpensively.

From a different point of view, another object of the invention is toprovide a novel-structure group III nitride compound semiconductordevice and a method for producing the device.

That is, according to the present invention, there is provided asemiconductor device comprising a substrate, an undercoat layer formedon the substrate and containing metal nitride, and a group III nitridecompound semiconductor layer formed on the undercoat layer. Suchsemiconductor device includes a light-emitting device, a photodetector,an electronic device, or the like.

The undercoat layer may be formed so as to contain at least one memberselected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride.

The substrate can be formed of any one member selected from the groupconsisting of sapphire, silicon carbide, gallium nitride, silicon,gallium phosphide, and gallium arsenide.

A titanium layer may be further provided between the undercoat layer andthe semiconductor layer.

A buffer layer of a group III nitride compound semiconductor may befurther provided between the semiconductor layer and the undercoatlayer.

Further, the undercoat layer may be constituted by a combination of atitanium layer formed on the substrate and a heat-resisting layer. Inthis case, the substrate is formed of silicon.

In the above description, the titanium layer and heat-resisting layermay be repeatedly alternately laminated one on another.

An electrode can be further provided on the undercoat layer.

In the semiconductor light-emitting device configured as described aboveaccording to the present invention, a GaN light-emitting layer is formedon the undercoat layer of metal nitride formed on the substrate. The GaNlight-emitting layer of a good crystal can be grown on the undercoatlayer because the lattice mismatch between the undercoat layer and thelight-emitting layer formed on the undercoat layer can be reduced byadjustment of the composition of metal nitride. On the other hand, thethickness of the undercoat layer can be reduced because the substratecan have a thickness required for holding the function of the device.Hence, the undercoat layer can be formed easily and inexpensively. If ageneral substrate such as a sapphire substrate is used as the substrate,the device can be produced inexpensively as a whole.

Moreover, in the configuration of the present invention, a reflectionlayer of metal nitride may be provided just under the light-emittinglayer. Light emitted from the light-emitting layer toward the substrateis reflected by the reflection layer because the reflection layer has agloss of metallic color so that the reflection layer reflects visiblelight. Further, the substantial whole of the light toward the substrateis reflected by the reflection layer because the reflection layer isdisposed just under the light-emitting layer. As a result, thesubstantial whole of the light emitted from the light-emitting layertoward the substrate can be utilized effectively, so that improvement ofthe brightness of the light-emitting device can be attained.

Features and advantages of the invention will be evident from thefollowing detailed description of the preferred embodiments described inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a view showing a light-emitting diode 1 as a first embodimentof the present invention;

FIG. 2 is a graph showing the relation between the substrate temperaturefor a TiN layer and the peak intensity of φ(PHI) scanning;

FIG. 3 is a graph showing the relation between the substrate temperaturefor a TiN layer formed on a sapphire substrate and the peak intensity ofφ(PHI) scanning of a GaN crystal grown on the TiN layer;

FIG. 4 is a graph showing the relation between the substrate temperaturefor a TiN layer formed through Al on an Si (111) substrate and the peakintensity of φ(PHI) scanning of a GaN crystal;

FIG. 5 shows an X-ray rocking curve of a GaN crystal on a buffer layerafter the buffer layer is formed on TiN;

FIG. 6 shows an X-ray rocking curve of a GaN crystal in the case wherethe GaN crystal is grown on TiN directly;

FIG. 7 is a graph showing the relation between the temperature for thegrowth of a buffer layer on TiN and the peak intensity of φ(PHI)scanning of a GaN crystal on the buffer layer;

FIG. 8 shows an X-ray rocking curve of a GaN layer formed on an AlNlayer of an sample 1 by an MOCVD method;

FIG. 9 is a view showing the configuration of a light-emitting diode asa second embodiment of the present invention;

FIG. 10 shows light-emitting characteristic of the light-emitting diodedepicted in FIG. 9;

FIG. 11 is a view showing the configuration of a light-emitting diode asa third embodiment of the present invention;

FIG. 12 is a view showing the configuration of a light-emitting diode asa fourth embodiment of the present invention;

FIG. 13 shows a result of φ(PHI) scanning of a sample 3;

FIG. 14 shows a result of φ(PHI) scanning of a sample 4;

FIG. 15 shows a result of φ(PHI) scanning of a sample 5;

FIG. 16 shows a result of φ(PHI) scanning of a sample 6;

FIG. 17 shows a result of φ(PHI) scanning of a sample 8;

FIG. 18 shows a result of φ(PHI) scanning of a sample 9;

FIG. 19 shows a result of φ(PHI) scanning of a sample 13;

FIG. 20 shows a result of φ(PHI) scanning of a sample 14;

FIG. 21 shows a result of φ(PHI) scanning of a sample 15;

FIG. 22 shows a result of φ(PHI) scanning of a sample 16;

FIG. 23 shows the configuration of a light-emitting diode as a fifthembodiment;

FIG. 24 shows the configuration of a light-emitting diode as a sixthembodiment;

FIG. 25 is a sectional view showing a light-emitting diode as a seventhembodiment; and

FIG. 26 is a sectional view showing a background-art light-emittingdiode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Respective constituent members of the present invention will bedescribed below.

A GaN semiconductor is a group III metal nitride semiconductor, which isgenerally represented by Al_(X)GaIn_(1−X−Y)N (0≦X≦1, 0≦Y≦1, X+Y≦1). Alayer of such a GaN semiconductor is grown by a known metal organicchemical vapor deposition method (hereinafter abbreviated as MOCVDmethod). Alternatively, this layer may be grown by a known molecularbeam epitaxy method (hereinafter abbreviated as MBE method), or thelike.

A hexagonal crystal material such as sapphire, SiC, or the like, or acubic crystal material such as Si, GaP, or the like, can be used as asubstrate. In the case of a hexagonal crystal material, a face c thereofis used.

When SiC, Si or GaP is used as a substrate, each of the substrate andthe metal nitride has electrically conducting characteristic. As aresult, electrodes can be formed at opposite ends of a semiconductorlight-emitting device, so that the “charge-up” problem can be solvedeasily.

This substrate needs characteristic (stiffness, impact resistance, etc.)for holding the function of the device. Hence, the substrate needs to benot thinner than about 100 μm.

The undercoat layer is formed of metal nitride. The metal nitride is notparticularly limited to a specific kind but nitride of Ti, Zr, Hf or Tacan be preferably used as the metal nitride. NbN, VN, YN, CrN, or thelike, may be used also as the metal nitride.

When these metal nitride compounds are used singly, lattice mismatchoccurs. For example, TiN makes a lattice mismatch of 6% for GaN and alattice mismatch of 3.5% for AlN, and similarly ZrN makes a latticemismatch of 1.5% for GaN and a lattice mismatch of 3.9% for AlN.Therefore, nitride of an alloy formed of these metals is preferably usedso that the undercoat layer of metal nitride makes a lattice match forthe light-emitting layer of metal nitride.

The method for growing the undercoat layer is not particularly limitedbut CVD (Chemical Vapor Deposition) such as plasma CVD, thermal CVD,optical CVD, etc., PVD (Physical Vapor Deposition) such as sputtering,reactive sputtering, laser ablation, ion plating, evaporation, etc., orthe like, may be used as the method.

The thickness of the undercoat layer is preferably set to be in a rangeof from 0.1 to 10 μm.

The undercoat layer may be grown through an appropriate buffer layer onthe substrate. The buffer layer may be a single layer or a laminateformed of a plurality of buffer layers.

Alternatively, a layer of a metal such as Ti, or the like, may belaminated on the aforementioned metal nitride to thereby form a Ti/metalnitride laminate as the undercoat layer.

Alternatively, the undercoat layer may be formed by means of repeating alaminate of metal nitride and a layer of a metal such as Ti, or thelike. In this case, preferably, the uppermost layer is formed of metalnitride.

The light-emitting layer is formed on the undercoat layer continuously.That is, the undercoat layer of metal nitride is disposed just under thelight-emitting layer. Hence, the substantial whole of light emitted fromthe light-emitting layer toward the substrate is reflected by theundercoat layer. As a result, the light emitted from the light-emittinglayer toward the substrate can be utilized effectively, so thatimprovement of the brightness of the light-emitting device can beattained.

A clad layer is formed on the light-emitting layer by a known method.After an necessary etching process, n-type and p-type electrodes areformed.

(First Embodiment)

A first embodiment of this invention will be described below withreference to the drawings.

FIG. 1 shows a light-emitting diode 1 according to this embodiment.Specifications of respective semiconductor layers are as follows.

Layer Composition Dopant (Thickness) p-type clad layer 6 p-GaN Mg (0.3μm) light-emitting layer 5 Superlattice structure quantum well layerIn_(0.15)Ga_(0.85)N (35 Å) barrier layer GaN (35 Å) the number ofrepeated quantum well and barrier layers: 1 to 10 reflection layer 4CTi_(0.268)Zr_(0.732)N (3000 Å) buffer layer 3 Al (100 Å) substrate 2Silicon (111) (300 μm)

The buffer layer 3 is laminated on the substrate 2 by an MOVPE method.

The reflection layer 4C is formed by a reactive sputtering method.Incidentally, in this embodiment, the reflection layer 4C serves also asan undercoat layer.

The light-emitting layer 5 is not limited to the superlattice structurebut the light-emitting layer 5 may be of a single hetero type, a doublehetero type, a homo-junction type, or the like.

An Al_(X)Ga_(Y)In_(1−X−Y)N (0≦X≦1, 0≦Y≦1, X+Y≦1) layer, which has a wideband gap and which is doped with an acceptor such as magnesium, or thelike, may be interposed between the light-emitting layer 5 and thep-type clad layer 6. This technique is employed for preventing electronsimplanted into the light-emitting layer 6 from being diffused into thep-type clad layer 6.

The p-type clad layer 6 may be of a double-layered structure with a p⁻layer of a low Mg density on the light-emitting layer 5 side and a p⁺layer of a high Mg density on the p-type electrode 8 side.

The respective semiconductor layers are formed by means of a known MOCVDmethod. In this growth method, an ammonia gas and gases of group IIImetal alkyl compounds such as trimethylgallium (TAG), trimethylaluminum(TMA) and trimethylindium (TMI) are supplied onto a substrate heated toan appropriate temperature and are subjected to a thermal decompositionreaction to thereby grow a desired crystal on the substrate.

A light-transmissible electrode 7, which is constituted by a thin filmcontaining gold, is laminated to cover the substantially whole area ofan upper face of the p-type clad layer 6. A p-type electrode 8, which isconstituted also by a material containing gold, is formed on thelight-transmissible electrode 7 by means of evaporation.

Incidentally, an n-type electrode 9 is formed on the Si substrate layer2 and bonded to a desired position.

This invention is not limited to the aforementioned description of themode for carrying out the invention and the embodiments thereof at all,and includes various modifications that can be conceived by thoseskilled in the art without departing from the scope of claim for apatent.

That is, the substrate is formed of a hexagonal crystal material or acubic crystal material. The undercoat layer may be formed on thesubstrate of the hexagonal crystal material or may be formed on a (111)face of the cubic crystal material.

Sapphire or silicon carbide may be used as the hexagonal crystalmaterial. Silicon or gallium phosphide may be used as the cubic crystalmaterial.

The metal nitride may contain at least one member selected from thegroup consisting of nitrides of Ti, Zr, Hf and Ta, and nitrides ofalloys of these metals.

The inventors of the present application have made further examinationeagerly to achieve at least one of the foregoing objects. As a result,the following invention has been conceived.

That is, a group III nitride compound semiconductor device comprising:

a substrate;

an undercoat layer formed on the substrate and containing at least onemember selected from the group consisting of titanium nitride, hafniumnitride, zirconium nitride, and tantalum nitride; and

a group III nitride compound semiconductor layer formed on the undercoatlayer.

In the semiconductor device configured as described above according tothe present invention, the undercoat layer of titanium nitride, hafniumnitride, zirconium nitride or tantalum nitride is formed on thesubstrate. The lattice mismatch between the undercoat layer of suchmetal nitride and the group III nitride compound semiconductor layerformed on the undercoat layer is reduced extremely. Hence, the group IIInitride compound semiconductor layer of a good crystal can be grown onthe undercoat layer. If a general substrate such as a sapphire substrateis used as the substrate, the device can be produced inexpensively as awhole.

In the above description, a hexagonal crystal material such as SiC(silicon carbide), GaN (gallium nitride), etc. or a cubic crystalmaterial such as Si (silicon), GaP (gallium phosphide), GaAs (galliumarsenide), etc. can be used as the substrate. In the case of a hexagonalcrystal material, the undercoat layer is grown on the hexagonal crystalmaterial. In the case of a cubic crystal material, a (111) face of thecubic crystal material is used.

When SiC, GaN, silicon, GaP or GaAs is used as the substrate,electrically conducting characteristic can be given to the substrate.Further, each of titanium nitride (TiN), hafnium nitride, zirconiumnitride and tantalum nitride has electrically conducting characteristic.As a result, electrodes can be formed at opposite faces of thesemiconductor device, so that the number of device process steps can bereduced to attain reduction of cost.

When an LED is produced by using sapphire as a substrate, metal nitridehas a metallic gloss. Hence, light emitted from the LED is reflected bytitanium nitride, hafnium nitride, zirconium nitride, etc., so that itis expected that brightness is improved.

This substrate needs characteristic (stiffness, impact resistance) forholding the function of the device. Therefore, the thickness of thesubstrate is set to substantially not less than 100 μm. Incidentally,the substrate may be thin if the stiffness of the substrate can be kept.

Among metal nitride compounds, titanium nitride, hafnium nitride,zirconium nitride or tantalum nitride is selected as the undercoatlayer. The method for growing these metal nitride compounds on apredetermined face of the substrate is not particularly limited but CVD(Chemical Vapor Deposition) such as plasma CVD, thermal CVD, opticalCVD, etc., PVD (Physical Vapor Deposition) such as sputtering, reactivesputtering, laser ablation, ion plating, evaporation, ECR, etc., or thelike, may be used as this method.

The thickness of the undercoat layer is preferably set to be in a rangeof from 50 Å to 10 μm.

Another layer may be interposed between the undercoat layer and thesubstrate. According to the inventors' examination, an Al layer ispreferably interposed between a (111) face of silicon and a titaniumnitride layer when titanium nitride is grown on the (111) face ofsilicon used as a substrate. The thickness of the Al layer is notparticularly limited but set to be about 100 Å. Also the method forforming the Al layer is not particularly limited but, for example, theAl layer is formed by means of evaporation or sputtering.

After the undercoat layer is formed on the substrate, the substrate ispreferably heated.

FIG. 2 shows a result of X-ray diffraction (φ(PHI) scanning) versus tothe temperature for heating in the case where a sapphire substrate isheated after titanium nitride (thickness: about 3000 Å) is formed on aface a of the sapphire substrate by a reactive sputtering method. Theheating time is 5 minutes. A quadraxial single crystal diffraction meter(product name: X-pert) made by Philips Corp. was used as an X-raydiffraction system (the same system will be applied to the followingresults of φ(PHI) scanning and X-ray rocking curve). See Journal ofElectronic Materials, Vol. 25, No. 11, pp. 1740-1747, 1996, concerningφ(PHI) scanning. In φ(PHI) scanning, peaks corresponding to crystalfaces are obtained when a sample is rotated by 360 degrees. In FIG. 2,the vertical axis shows the average value of the peak intensity of TiNlayer (relative values). Because samples in which thicknesses of TiNlayers are made uniform are used for measurement, it is thought of thatthe larger the intensity is, the better crystal is obtained. It isthought of that the crystallinity of the group III nitride compoundsemiconductor layer grown on the undercoat layer becomes better as thecrystallinity of titanium nitride of the undercoat layer becomes better.

FIG. 3 shows a result of φ(PHI) scanning of a GaN layer which is formedon a titanium nitride undercoat layer by an MOCVD method after titaniumnitride grown in the same condition as described above is heated (for 5minutes) in an atmosphere of hydrogen.

It is preferable from the results shown in FIGS. 2 and 3 that thetemperature for heating the undercoat layer is set to be in a range offrom 600 to 1200° C. It is thought of that such heating improves thecrystallinity of the undercoat layer more greatly. More preferably, thetemperature for heating is in a range of from 800 to 1200° C.

It is preferable from the result shown in FIG. 2 that the undercoatlayer is heated in an atmosphere of hydrogen or in a vacuum. Morepreferably, it is heated in an atmosphere of hydrogen.

A titanium nitride layer (thickness: about 3000 Å, growth method:reactive sputtering method) is formed through an Al layer (thickness:about 100 Å) on a (111) face of a silicon substrate. Then, a GaN layeris formed on the titanium nitride layer in the same manner as in FIG. 2.FIG. 4 shows a result of φ(PHI) scanning of this GaN layer.

It is apparent from the result shown in FIG. 4 that the temperature forheating is set to be preferably in a range of from 600 to 1200° C., morepreferably in a range of from 800 to 1200° C.

The group III nitride compound semiconductor is represented by thegeneral formula Al_(X)Ga_(Y)In_(1−X−Y)N (0≦X≦1, 0≦Y≦1, 0≦X+Y≦1), whichmay further contain group III elements such as boron (B) and thallium(Tl) and in which the nitrogen (N) may be partially replaced byphosphorus (P), arsenic (As), antimony (Sb) or bismuth (Bi). The groupIII nitride compound semiconductor may contain an optional dopant.

As is commonly known, a light-emitting device or a photodetector isconfigured so that different electrically conductive types of group IIInitride compound semiconductor layers are laminated. A superlatticestructure, a double heterostructure, or the like, is applied thereto. Anelectronic device represented by an FET structure can be also formedfrom group III nitride compound semiconductors. In this manner, theplurality of group III nitride compound semiconductor layers formed onthe undercoat layer act on one another to fulfil a desired function.

For example, a titanium layer may be interposed between the undercoatlayer and the group III nitride compound semiconductor layer accordingto the present invention. According to the inventors' examinationreferred in Japanese Patent Publication No. Hei. 11-195814 which isincorporated herein by reference, it has been found that the crystalstructure of the group III nitride compound semiconductor layer formedon the titanium layer becomes good. The thickness of the titanium layerand the method for forming the titanium layer are not particularlylimited.

A buffer layer may be preferably formed between the undercoat layer ofmetal nitride and the group III nitride compound semiconductor layer (ofa second group III nitride compound semiconductor) constituting thedevice function portion. The buffer layer is formed of a first group IIInitride compound semiconductor. The concept “first group III nitridecompound semiconductor” used here includes quaternary compoundsemiconductors represented by Al_(X)Ga_(Y)In_(1−X−Y)N (0<X<1, 0<Y<1,0<X+Y<1), ternary compound semiconductors represented by Al_(X)Ga_(1−X)N(0<X<1), Al_(X)In_(1−X)N (0<X<1), Ga_(X)In_(1−X)N (0<X<1), and binarycompound semiconductors AlN, GaN and InN.

When GaN is to be grown on metal nitride, a GaN crystal can be growneven in the case where there is no buffer layer but a better GaN crystalcan be provided in the case where there is a buffer layer (see FIGS. 5and 6).

Incidentally, FIG. 5 shows an X-ray rocking curve of a GaN crystal inthe case where a buffer layer of AlN (thickness: 600 Å, growthtemperature: 1000° C.) and a GaN layer (thickness: 1 μm, growthtemperature: 1000° C.) are formed successively on an undercoat layer oftitanium nitride (thickness: 3000 Å, substrate: sapphire) by an MOCVDmethod. On the other hand, FIG. 6 shows an X-ray rocking curve of a GaNcrystal in the case where a GaN layer is formed in the aforementionedmanner without formation of any buffer layer of AlN.

FIG. 7 shows the relation between the crystallinity (vertical axis:X-ray diffraction intensity (average value of PHI scanning)) of a GaNlayer (thickness: 1 μm, growth temperature: 1000° C.) formed on a bufferlayer of AlN (thickness: 600 Å) and the temperature for the growth ofthe buffer layer in the case where the buffer layer is formed on anundercoat layer of titanium nitride (thickness: 3000 Å, substrate:sapphire) by an MOCVD method while the temperature for the growth of thebuffer layer is changed.

It is apparent from FIG. 7 that a more excellent result is obtained asthe growth temperature for forming the buffer layer by means of theMOCVD method becomes higher (FIG. 7).

In a general MOCVD method, the first group III nitride compoundsemiconductor layer (buffer layer) of AlN, GaN, or the like, was formeddirectly on a substrate of sapphire, or the like, at a low temperatureof about 400° C. When an undercoat layer of metal nitride is formed onthe substrate, a better crystal can be, however, obtained by means ofgrowing the first group III nitride compound semiconductor at a hightemperature of about 1000° C. Hence, the crystallinity of the secondgroup III nitride compound semiconductor layer formed on the bufferlayer of good crystallinity is also improved.

The temperature of about 1000° C. is substantially equal to thetemperature for the growth of the second group III nitride compoundsemiconductor layer (device function constituting layer) formed on thefirst group III nitride compound semiconductor layer (buffer layer).Hence, the growth temperature for forming the first group III nitridecompound semiconductor by means of the MOCVD method is set to bepreferably in a range of from 600 to 1200° C., more preferably in arange of from 800 to 1200° C.

When the temperature for the growth of the first group III nitridecompound semiconductor layer (buffer layer) is equal to the temperaturefor the growth of the second group III nitride compound semiconductorlayer (device function constituting layer) as described above,temperature control for executing the MOCVD method is made easily.

Also in the case where the buffer layer constituted by the first groupIII nitride compound semiconductor layer is formed on the undercoatlayer by a sputtering method, the crystallinity of the obtained bufferlayer is equal to or more excellent than that in the case where thebuffer layer is formed by an MOCVD method. Hence, the crystallinity ofthe second group III nitride compound semiconductor layer formed on thefirst group III nitride compound semiconductor layer is also improved(see FIG. 8). Moreover, when the first group III nitride compoundsemiconductor layer (buffer layer) is formed by a sputtering method,expensive metal organic compounds such as TMA, TMI, etc. need not beused as raw materials compared with the MOCVD method. Hence, the devicecan be formed inexpensively.

Samples for evaluating improvement in crystallinity of the first groupIII nitride compound semiconductor and the second group III nitridecompound semiconductor formed thereon as described in the aboveparagraph will be described below.

Sample 1

An undercoat layer of titanium nitride (thickness: 3000 Å) was formed ona sapphire substrate by a reactive DC magnetron spattering method whileusing titanium as a target and introducing a nitrogen gas. Then, thetarget was exchanged to aluminum and a reactive DC magnetron sputteringmethod was executed to thereby form a buffer layer of AlN (thickness:600 Å).

From the result of φ(PHI) scanning in measurement by an X-raydiffraction system adjusted to a (200) face of the undercoat layer(titanium nitride) and the result of φ(PHI) scanning of a (10-12) faceof the buffer layer (AlN), six symmetrical peaks were confirmed in eachscanning. Hence, TiN and AlN films having crystallinity of a singlecrystal or near to a single crystal were formed.

If this statement is amplified, a first group III nitride compoundsemiconductor layer formed, by a sputtering method, on an undercoatlayer containing at least one member selected from the group consistingof metal nitride compounds, that is, titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride has good crystallinitysufficiently to grow a second group III nitride compound semiconductorconstituting the device function portion on the first group III nitridecompound semiconductor layer.

Evaluation in the case where a silicon substrate was used was made inthe same manner as described above. The evaluation will be describedbelow.

Sample 2

An Al layer (100 Å) was formed on a silicon substrate by means ofevaporation. Then, an undercoat layer of titanium nitride (thickness:3000 Å) was formed on the Al layer by a reactive DC magnetron sputteringmethod while using titanium as a target and introducing a nitrogen gas.Then, the target was exchanged to aluminum and a reactive DC magnetronsputtering method was executed to thereby form a buffer layer of AlN(thickness: 600 Å).

From the result of φ(PHI) scanning of a (200) face of the undercoatlayer (titanium nitride) in this sample and the result of φ(PHI)scanning of a (10-12) face of the buffer layer (AlN) in this sample, sixsymmetrical peaks were confirmed in each scanning. Hence, it wasapparent that the crystal of each of titanium nitride and the bufferlayer of AlN was a single crystal or a crystal near to the singlecrystal oriented to an axis c.

If this statement is amplified, a first group III nitride compoundsemiconductor layer formed, by a sputtering method, on an undercoatlayer containing at least one member selected from the group consistingof metal nitride compounds, that is, titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride has good crystallinitysufficiently to grow a second group III nitride compound semiconductorconstituting the device function portion on the first group III nitridecompound semiconductor layer.

It is further apparent from these results that the quality of thesubstrate material is insignificant.

FIG. 8 shows an X-ray rocking curve of an GaN layer in the case wherethe GaN layer (thickness: 2.5 μm) is further formed on the sample 1 byan MOCVD method (growth temperature: 1100° C.). The half-value width ofthe rocking curve is 19 s. Hence, it is apparent that the quality of theGaN layer is high.

In the sample 1, the GaN layer was formed on the AlN layer in theaforementioned condition while changing the thicknesses of the titaniumnitride and AlN layers. The X-ray rocking curve of the GaN layer wasmeasured. The following table shows a result thereof.

GaN X-ray Rocking Curve AlN Film Thickness Å 600 800 1000 1200 1500 2000TiN Film 1500 19s 18s 22s Thickness Å 3000 19s 21s 21s 22s 21s 23s

From the result shown in the above, the GaN layer of good crystallinitywas obtained regardless of the thicknesses of the titanium nitride andAlN layers.

If this statement is amplified, a second group III nitride compoundsemiconductor (device function portion) with good crystallinity can begrown on a first group III nitride compound semiconductor layer (bufferlayer) regardless of the thicknesses of undercoat and buffer layers inthe case where the first group III nitride compound semiconductor layer(buffer layer) is formed on an undercoat layer containing at least onemember selected from the group consisting of metal nitride compounds,that is, titanium nitride, zirconium nitride, hafnium nitride, andtantalum nitride by an MOCVD method (growth temperature: 600 to 1200° C.or equal to the temperature for the growth of the second group IIInitride compound semiconductor) or by a sputtering method.

(Second Embodiment)

A second embodiment of this invention will be described below.

This embodiment shows a light-emitting diode 10. FIG. 9 shows theconfiguration of the light-emitting diode 10.

Specifications of respective layers are as follows.

Layer Composition Dopant (Thickness) p-type clad layer 18 p-GaN Mg (0.3μm) light-emitting layer 17 superlattice structure quantum well layerIn_(0.15)Ga_(0.85)N (35 Å) barrier layer GaN (35 Å) the number ofrepeated quantum well and barrier layers: 1 to 10 n-type clad layer 16n-GaN Si (4 μm) buffer layer 15 AlN (600 Å) TiN layer 14 TiN single(3000 Å) crystal substrate 11a sapphire (300 μm)

The n-type clad layer 16 may be of a double-layered structure with an n⁻layer of a low electron density on the light-emitting layer 17 side andan n+layer of a high electron density on the buffer layer 15 side.

The light-emitting layer 17 is not limited to the superlatticestructure. A single hetero type, a double hetero type, a homo-junctiontype, or the like, can be used as the configuration of thelight-emitting device.

An Al_(X)In_(Y)Ga_(1−X−Y)N (inclusive of X=0, Y=0, X=Y=0) layer, whichhas a wide band gap and which is doped with an acceptor such asmagnesium, or the like, may be interposed between the light-emittinglayer 17 and the p-type clad layer 18. This technique is used forpreventing electrons implanted into the light-emitting layer 17 frombeing diffused into the p-type clad layer 18.

The p-type clad layer 18 may be of a double-layered structure with a p⁻layer of a low hole density on the light-emitting layer 17 side and a p⁺layer of a high hole density on the electrode side.

The TiN layer 14 is formed on a face a of the sapphire substrate by areactive DC magnetron sputtering method. Further, the target isexchanged to Al and an AlN layer is formed by a reactive DC magnetronsputtering method.

Then, the AlN/TiN/sapphire sample is transferred from a spatteringapparatus into a chamber of an MOCVD apparatus. While a hydrogen gas ismade to flow into the chamber, the sample is heated to 1100° C. and keptat 1100° C. for 5 minutes.

Then, in the condition that the temperature is kept 1100° C., the secondgroup III nitride compound semiconductor layer containing the n-typeclad layer 16 and layers following the n-type clad layer 16 is formed inaccordance with an ordinary method (MOCVD method). In this growthmethod, an ammonia gas and gasses of group III metal alkyl compoundssuch as trimethylgallium (TAG), trimethylaluminum (TMA), andtrimethylindium (TMI) are supplied to a substrate that has been heatedto an appropriate temperature and are subjected to a thermaldecomposition reaction to thereby grow a desired crystal on thesubstrate.

The crystallinity of the second group III nitride compound semiconductorlayer formed in the aforementioned manner in this embodiment isexcellent.

A light-transmissible electrode 19, which is constituted by a thin filmcontaining gold, is laminated to cover the substantially almost wholearea of an upper face of the p-type clad layer 18. A p-type electrode20, which is constituted also by a material containing gold, is formedon the light-transmissible electrode 19 by means of evaporation.

An n-type electrode 21 is formed by means of evaporation onto a face ofthe n-GaN layer 16 revealed by means of etching.

When currents of 20, 50 and 100 mA were applied to the light-emittingdiode 10 configured as shown in FIG. 9, light emission (EL spectrum)shown in FIG. 10 was achieved. When the light-emitting diode 10 wasenclosed in a cannonball type package, emission light intensity of 1 cdor larger was exhibited.

(Third Embodiment)

FIG. 11 shows a light-emitting diode 22 as a third embodiment.Incidentally, the same parts as shown in the second embodiment arereferred to by the same characters so that the description thereof willbe omitted.

Layer Composition Dopant (Thickness) p-type clad layer 18 p-GaN Mg (0.3μm) light-emitting layer 17 superlattice structure Quantum well layerIn_(0.15)Ga_(0.85)N (35 Å) Barrier layer GaN (35 Å) the number ofrepeated quantum well and barrier layers: 1 to 10 n-type clad layer 16n-GaN Si (4 μm) Buffer layer 15 AlN (600 Å) TiN layer 14 TiN single(3000 Å) crystal Al layer 12 Al (100 Å) Substrate 11 Si (111) (300 μm)

The Al layer formed on an Si (111) face is epitaxially grown by ageneral method, that is, by an evaporation method or by a sputteringmethod.

The method for the growth of the TiN layer 14 and layers following theTiN layer 14 is the same as in the second embodiment.

Incidentally, an n-type electrode 30 is formed on the Si substrate layer11 and bonded to desired position.

(Fourth Embodiment)

FIG. 12 shows a semiconductor device as a fourth embodiment of thisinvention. The semiconductor device in this embodiment is alight-emitting diode 32. Incidentally, the same parts as shown in FIG.11 are referred to by the same characters so that the descriptionthereof will be omitted.

Specifications of respective layers are as follows.

Layer Composition Dopant (Thickness) n-type clad layer 28 n-GaN Si (0.3μm) Light-emitting layer 17 superlattice structure Quantum well layerIn_(0.15)Ga_(0.85)N (35 Å) Barrier layer GaN (35 Å) The number ofrepeated quantum well and barrier layers: 1 to 10 p-type clad layer 26p-GaN Mg (4 μm) Buffer layer 15 AlN (600 Å) TiN layer 14 TiN single(3000 Å) crystal Al layer 12 Al (100 Å) Substrate 11 Si (111) (300 μm)

As shown in FIG. 12, the p-type clad layer 26, the light-emitting layer17 and the n-type clad layer 28 are grown successively on the bufferlayer 15 to thereby form the light-emitting diode 32. In the case ofthis device 32, the light-transmissible electrode (see the referencecharacter 19 in FIG. 11) can be omitted because the n-type clad layer 28of low resistance is provided as the uppermost face.

In FIG. 12, the reference character 30 designates an n-type electrode. Ap-type electrode 20 is formed on the Si substrate 11.

Although the aforementioned embodiments have shown the case where thebuffer layer is formed by a DC magnetron sputtering method, theinvention may be applied also to the case where the buffer layer isformed by an MOCVD method, or the like, (if the growth temperature is ashigh as 1000° C.).

The device to which the present invention is applied is not limited tothe aforementioned light-emitting diode. The present invention may beapplied also to optical devices such as a photodetector, a laser diode,a solar cell, etc., bipolar devices such as a rectifier, a thyristor, atransistor, etc., unipolar devices such as an FET, etc., and electronicdevices such as a microwave device, etc.

The present invention may be further applied to laminates which areintermediates of these devices.

This invention is not limited to the aforementioned description of themode for carrying out the invention and embodiments thereof at all, andincludes various modifications that can be conceived by those skilled inthe art without departing from the scope of claim for a patent.

The following items will be disclosed hereunder.

-   (11) A laminate comprising:

a substrate;

an undercoat layer formed on the substrate and containing at least onemember selected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride; and

a group III nitride compound semiconductor layer formed on the undercoatlayer.

-   (12) A laminate according to the paragraph (11), wherein the    substrate is made of any one of sapphire, silicon carbide, gallium    nitride, silicon, gallium phosphide, and gallium arsenide.-   (13) A laminate according to the paragraph (11) or (12), wherein the    substrate is constituted by a cubic crystal material with a (111)    face or a hexagonal crystal material on which the undercoat layer is    formed.-   (14) A laminate according to any one of the paragraphs (11) to (13),    wherein a titanium layer is interposed between the undercoat layer    and the group III nitride compound semiconductor layer.-   (15) A laminate according to any one of the paragraphs (11) to (14),    wherein the undercoat layer is heated at a temperature of from 600    to 1200 before the group III nitride compound semiconductor layer is    formed.-   (16) A laminate according to any one of the paragraphs (11) to (15),    wherein the group III nitride compound semiconductor layer is a    buffer layer.-   (17) A laminate according to the paragraph (16), wherein:

a second group III nitride compound semiconductor layer to form a devicefunction portion on the buffer layer; and

the buffer layer is formed by an MOCVD method at a temperaturesubstantially equal to or higher than the temperature for the growth ofthe second group III nitride compound semiconductor layer.

-   (18) A laminate according to the paragraph (16), wherein the buffer    layer is formed by any one of a sputtering method, a vapor    deposition method, and an ion plating method.-   (21) A method of producing a group III nitride compound    semiconductor device, comprising the steps of: forming an undercoat    layer, which contains at least one member selected from the group    consisting of titanium nitride, zirconium nitride, hafnium nitride,    and tantalum nitride, on a substrate; heating the undercoat layer at    a temperature of from 600 to 1200° C.; and forming a group III    nitride compound semiconductor layer on the undercoat layer.-   (22) A producing method according to the paragraph (21), wherein the    temperature used for the heating is from 800 to 1200° C.-   (23) A producing method according to the paragraph (21) or (22),    wherein the heating is performed in a hydrogen gas.-   (24) A producing method according to the paragraph (21) or (22),    wherein the heating is performed in a vacuum.-   (31) A group III nitride compound semiconductor device comprising:

a substrate;

an undercoat layer formed on the substrate and containing at least onemember selected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride; and

a group III nitride compound semiconductor layer formed on the undercoatlayer,

wherein the undercoat layer is subjected to heat treatment attemperature from 600 to 1200° C.

-   (32) A device according to the paragraph (31), wherein the    temperature used for the heating is from 800 to 1200° C.-   (33) A device according to the paragraph (31) or (32), wherein the    heating is performed in a hydrogen gas.-   (34) A device according to the paragraph (31) or (32), wherein the    heating is performed in a vacuum.-   (41) A method of producing a laminate comprising the steps of:    forming an undercoat layer on a substrate, said under coat layer    containing at least one member selected from the group consisting of    titanium nitride, zirconium nitride, hafnium nitride, and tantalum    nitride; and

heating the undercoat layer at temperature from 600 to 1200° C. to forma group III nitride compound semiconductor layer on the undercoat layer.

-   (42) A producing method according to the paragraph (41), wherein the    temperature used for the heating is from 800 to 1200° C.-   (43) A producing method according to the paragraph (41) or (42),    wherein the heating is performed in a hydrogen gas.-   (44) A device according to the paragraph (41) or (42), wherein the    heating is performed in a vacuum.-   (51) A laminate comprising:

a substrate;

an undercoat layer formed on the substrate and containing at least onemember selected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride; and

a group III nitride compound semiconductor layer formed on the undercoatlayer,

wherein the undercoat layer is subjected to heat treatment attemperature from 600 to 1200° C.

-   (52) A laminate according to the paragraph (51), wherein the    temperature used for the heating is from 800 to 1200° C.-   (53) A laminate according to the paragraph (51) or (52), wherein the    heating is performed in a hydrogen gas.-   (54) A laminate according to the paragraph (51) or (52), wherein the    heating is performed in a vacuum.-   (61) A method of producing a group III nitride compound    semiconductor device, comprising the steps of: preparing a substrate    having an undercoat layer containing at least one member selected    from the group consisting of titanium nitride, zirconium nitride,    hafnium nitride, and tantalum nitride; and forming a buffer layer of    a first group III nitride compound semiconductor layer on the    undercoat layer by an MOCVD method at a temperature substantially    equal to or higher than the temperature for the growth of a second    group III nitride compound semiconductor layer which will be formed    thereafter by an MOCVD method so as to constitute a device function    portion.-   (62) A method of producing a group III nitride compound    semiconductor device, comprising the steps of: preparing a substrate    having an undercoat layer containing at least one member selected    from the group consisting of titanium nitride, zirconium nitride,    hafnium nitride, and tantalum nitride; forming a buffer layer of a    first group III nitride compound semiconductor layer on the    undercoat layer by an MOCVD method at a temperature of from 600 to    1200° C.; and forming a second group III nitride compound    semiconductor layer on the buffer layer.-   (63) A producing method according to the paragraph (62), wherein the    temperature for the growth of the buffer layer is from 800 to 1200°    C.-   (64) A producing method according to the paragraph (62), wherein the    temperature for the growth of the buffer layer is about 1000° C.-   (65) A producing method according to any one of the paragraphs (61)    to (64), wherein the buffer layer is formed of Al_(a)Ga_(1−a)N    (0≦a≦1).-   (66) A producing method according to any one of the paragraphs (61)    to (64), wherein the buffer layer is formed of AlN.-   (67) A producing method according to any one of the paragraphs (61)    to (64), wherein: the undercoat layer is formed of titanium nitride;    and the buffer layer is formed of AlN.-   (68) A producing method according to any one of the paragraphs (61)    to (67), wherein the undercoat layer is heated before the buffer    layer is formed.-   (69) A producing method according to the paragraph (68), wherein the    heating is performed in a hydrogen gas or in a vacuum.-   (71) A group III nitride compound semiconductor device comprising:

a substrate having an undercoat layer containing at least one memberselected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride;

a buffer layer of a first group III nitride compound semiconductor layerformed on the undercoat layer; and

a second group III nitride compound semiconductor layer formed on saidbuffer layer and for constituting a device function portion;

wherein said buffer layer is formed by an MOCVD method at a temperaturesubstantially equal to or higher than the temperature for the growth ofthe second group III nitride compound semiconductor layer.

-   (72) A group III nitride compound semiconductor device comprising:

a substrate having an undercoat layer containing at least one memberselected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride;

a buffer layer of a first group III nitride compound semiconductor layerformed on the undercoat layer;

a second group III nitride compound semiconductor layer formed on saidbuffer layer and constituting a device function portion;

wherein said buffer layer is formed by an MOCVD method at a temperaturefor the growth from 600 to 1200° C.

-   (73) A device according to the paragraph (72), wherein the    temperature for the growth of the buffer layer is from 800 to 1200°    C.-   (74) A device according to the paragraph (72), wherein the    temperature for the growth of the buffer layer is about 1000° C.-   (75) A device according to any one of the paragraphs (71) to (74),    wherein the buffer layer is formed of Al_(a)Ga_(1−a)N (0≦a≦1).-   (76) A device according to any one of the paragraphs (71) to (74),    wherein the buffer layer is formed of AlN.-   (77) A device according to any one of the paragraphs (71) to (74),    wherein: the undercoat layer is formed of titanium nitride; and the    buffer layer is formed of AlN.-   (78) A device according to any one of the paragraphs (71) to (77),    wherein the undercoat layer is heated before the buffer layer is    formed.-   (79) A device according to the paragraph (78), wherein the heating    is performed in an atmosphere of hydrogen or in a vacuum.-   (81) A method of producing a laminate comprising the steps of:

preparing a substrate having an undercoat layer containing at least onemember selected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride; and

forming a buffer layer of a first group III nitride compoundsemiconductor layer on the undercoat layer by a MOCVD method at atemperature substantially equal to or higher than the temperature forthe growth of a second group III nitride compound semiconductor layerwhich will be formed thereafter by a MOCVD method.

-   (82) A method of producing a laminate, comprising the steps of:

preparing a substrate having an undercoat layer containing at least onemember selected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride;

forming a buffer layer of a first group III nitride compoundsemiconductor layer on the undercoat layer by an MOCVD method at atemperature of from 600 to 1200° C.; and

forming a second group III nitride compound semiconductor layer on thebuffer layer.

-   (83) A producing method according to the paragraph (82), wherein the    temperature for the growth of the buffer layer is from 800 to 1200°    C.-   (84) A producing method according to the paragraph (82), wherein the    temperature for the growth of the buffer layer is about 1000° C.-   (85) A producing method according to any one of the paragraphs (81)    to (84), wherein the buffer layer is formed of Al_(a)Ga_(1−a)N    (0≦a≦1).-   (86) A producing method according to any one of the paragraphs (81)    to (84), wherein the buffer layer is formed of AlN.-   (87) A producing method according to any one of the paragraphs (81)    to (84), wherein: the undercoat layer is formed of titanium nitride;    and the buffer layer is formed of AlN.-   (88) A producing method according to any one of the paragraphs (81)    to (87), wherein the undercoat layer is heated before the buffer    layer is formed.-   (89) A producing method according to the paragraph (88), wherein the    heating is performed in a hydrogen gas or in a vacuum.-   (91) A laminate comprising:

a substrate having an undercoat layer containing at least one memberselected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride;

a buffer layer of a first group III nitride compound semiconductor layerformed on the undercoat layer; and

a second group III nitride compound semiconductor layer formed on saidbuffer layer and for constituting a device function portion;

wherein said buffer layer is formed by an MOCVD method at a temperaturesubstantially equal to or higher than the temperature for the growth ofthe second group III nitride compound semiconductor layer.

-   (92) A laminate comprising:

a substrate having an undercoat layer containing at least one memberselected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride;

a buffer layer of a first group III nitride compound semiconductor layerformed on the undercoat layer;

a second group III nitride compound semiconductor layer formed on saidbuffer layer and constituting a device function portion;

wherein said buffer layer is formed by an MOCVD method at a temperaturefor the growth from 600 to 1200° C.

-   (93) A laminate according to the paragraph (92), wherein the    temperature for the growth of the buffer layer is from 800 to 1200°    C.-   (94) A laminate according to the paragraph (92), wherein the    temperature for the growth of the buffer layer is about 1000° C.-   (95) A laminate according to any one of the paragraphs (91) to (94),    wherein the buffer layer is formed of Al_(a)Ga_(1−a)N (0≦a≦1).-   (96) A laminate according to any one of the paragraphs (91) to (94),    wherein the buffer layer is formed of AlN.-   (97) A laminate according to any one of the paragraphs (91) to (94),    wherein: the undercoat layer is formed of titanium nitride; and the    buffer layer is formed of AlN.-   (98) A laminate according to any one of the paragraphs (91) to (97),    wherein the undercoat layer is heated before the buffer layer is    formed.-   (99) A laminate according to the paragraph (98), wherein the heating    is performed in a hydrogen gas or in a vacuum.-   (101) A method of producing a group III nitride compound    semiconductor device, comprising the steps of:

preparing a substrate having an undercoat layer containing at least onemember selected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride;

forming a buffer layer of a first group III nitride compoundsemiconductor layer on the undercoat layer by a method other than anMOCVD method; and

forming a second group III nitride compound semiconductor layerconstituting a device function portion on the buffer layer.

-   (102) A producing method according to the paragraph (101), wherein    the buffer layer is formed of Al_(a)Ga_(1−a)N (0≦a≦1).-   (103) A producing method according to the paragraph (101), wherein    the buffer layer is formed of AlN.-   (104) A producing method according to (101), wherein: the undercoat    layer is formed of titanium nitride; and the buffer layer is formed    of AlN.-   (105) A producing method according to the paragraph (101), wherein    the buffer layer is formed by DC magnetron sputter method.-   (106) A producing method according to any one of the    paragraphs (101) to (105), wherein the substrate having the    undercoat layer is heated before the buffer layer is formed.-   (107) A producing method according to the paragraph (106), wherein    the heating is performed in a hydrogen gas or in a vacuum.-   (108) A producing method according to any one of the    paragraphs (101) to (107), wherein the buffer layer formed on the    undercoat layer is heated in an atmosphere of a mixture of a    hydrogen gas and an ammonia gas, and thereafter the second group III    nitride compound semiconductor layer is formed.-   (111) A group III nitride compound semiconductor device, comprising:

a substrate having an undercoat layer of metal nitride;

a buffer layer formed on the undercoat layer and made of a first groupIII nitride compound semiconductor layer;

a second group III nitride compound semiconductor layer formed on thebuffer layer and for constituting a device function portion;

wherein the buffer layer is formed by a method other than an MOCVDmethod.

-   (112) A device according to the paragraph (111), wherein the buffer    layer is formed of Al_(a)Ga_(1−a)N (0≦a≦1).-   (113) A device according to the paragraph (111), wherein the buffer    layer is formed of AlN.-   (114) A device according to (111), wherein: the undercoat layer is    formed of titanium nitride; and the buffer layer is formed of AlN.-   (115) A device according to the paragraph (111), wherein the buffer    layer is formed by DC magnetron sputter method.-   (116) A device according to any one of the paragraphs (111) to    (115), wherein the substrate having the undercoat layer is heated    before the buffer layer is formed.-   (117) A device according to the paragraph (116), wherein the heating    is performed in a hydrogen gas or in a vacuum.-   (118) A device according to any one of the paragraphs (111) to    (117), wherein the buffer layer formed on the undercoat layer is    heated in an atmosphere of a mixture of a hydrogen gas and an    ammonia gas, and thereafter the second group III nitride compound    semiconductor layer is formed.-   (121) A method of producing a laminate comprising the steps of:

preparing a substrate having an undercoat layer containing at least onemember selected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride;

forming a buffer layer of a first group III nitride compoundsemiconductor layer formed on the metal nitride undercoat layer by amethod other than an MOCVD method; and

forming a second group III nitride compound semiconductor layerconstituting a device function portion on the buffer layer.

-   (122) A producing method according to the paragraph (121), wherein    the buffer layer is formed of Al_(a)Ga_(1−a)N (0≦a≦1).-   (123) A producing method according to the paragraph (121), wherein    the buffer layer is formed of AlN.-   (124) A producing method according to (121), wherein: the undercoat    layer is formed of titanium nitride; and the buffer layer is formed    of AlN.-   (125) A producing method according to the paragraph (121), wherein    the buffer layer is formed by DC magnetron sputter method.-   (126) A producing method according to any one of the    paragraphs (121) to (125), wherein the substrate having the    undercoat layer is heated before the buffer layer is formed.-   (127) A producing method according to the paragraph (126), wherein    the heating is performed in an atmosphere of hydrogen or in a    vacuum.-   (128) A producing method according to any one of the    paragraphs (121) to (127), wherein the buffer layer formed on the    undercoat layer is heated in an atmosphere of a mixture of a    hydrogen gas and an ammonia gas, and thereafter the second group III    nitride compound semiconductor layer is formed.-   (131) A laminate comprising:

a substrate having an undercoat layer containing at least one memberselected from the group consisting of titanium nitride, zirconiumnitride, hafnium nitride, and tantalum nitride;

a buffer layer of a first group III nitride compound semiconductor layerformed on the undercoat layer; and

a second group III nitride compound semiconductor layer constituting adevice function portion on the buffer layer;

wherein the buffer layer is formed by a method other than an MOCVDmethod.

-   (132) A laminate according to the paragraph (131), wherein the    buffer layer is formed of Al_(a)Ga_(1−a)N (0≦a≦1).-   (133) A laminate according to the paragraph (131), wherein the    buffer layer is formed of AlN.-   (134) A laminate according to (131), wherein: the undercoat layer is    formed of titanium nitride; and the buffer layer is formed of AlN.-   (135) A laminate according to the paragraph (131), wherein the    buffer layer is formed by DC magnetron sputter method.-   (136) A laminate according to any one of the paragraphs (131) to    (135), wherein the substrate having the undercoat layer is heated    before the buffer layer is formed.-   (137) A producing method according to the paragraph (136), wherein    the heating is performed in an atmosphere of hydrogen or in a    vacuum.-   (138) A laminate according to any one of the paragraphs (131) to    (137), wherein the buffer layer formed on the undercoat layer is    heated in an atmosphere of a mixture of a hydrogen gas and an    ammonia gas, and thereafter the second group III nitride compound    semiconductor layer is formed.

The inventors of the present application have made examination eagerlyto find a novel substrate adapted for the growth of a GaN semiconductorlayer. As a result, the inventors have conceived the followingparagraphs and disclosed them in Japanese Patent Publication No. Hei.11-195814 which is incorporated herein by reference.

That is, the inventors have conclusively conceived that the substratemust satisfy at least two of the following requirements {circle around(1)} to {circle around (5)} for hetero epitaxial growth of a GaNsemiconductor on the substrate.

-   {circle around (1)} The adherence between the GaN semiconductor and    the substrate is good;-   {circle around (2)} The thermal expansion coefficient of the GaN    semiconductor is near to that of the substrate;-   {circle around (3)} The elastic modulus of the substrate is low;-   {circle around (4)} The crystal structure of the substrate is equal    to that of the GaN semiconductor; and-   {circle around (5)} The ratio of the absolute value of the    difference between the lattice constant of the substrate and the    lattice constant of the GaN semiconductor to the lattice constant of    the GaN semiconductor is not larger than 0.05 (that is, the    difference between the lattice constant of the substrate and the    lattice constant of the GaN semiconductor is not larger than ±5%).

It is a matter of course that the substrate may satisfy preferably atleast three of the five requirements, more preferably at least four ofthe five requirements, most preferably all the five requirements.

In the aforementioned Japanese Patent Publication No. 11-195814,attention has been paid to several metal materials as materialssatisfying the aforementioned condition. Ti has been disclosed as one ofthe metal materials.

According to the aforementioned Patent Application, at least a surfaceof the substrate, that is, a substrate's face touching the GaNsemiconductor layer must satisfy the aforementioned requirements.

Hence, the base portion of the substrate can be formed from an optionalmaterial and the surface portion of the substrate can be formed from amaterial satisfying the aforementioned requirements.

A buffer layer of Al_(a)In_(b)Ga_(1−a−b)N (inclusive of a=0, b=0, a=b=0)such as AlN or GaN can be interposed between the semiconductor layer andthe substrate in the same manner as in the case of a sapphire substrate.

On the other hand, according to Japanese Patent Publication No.11-195814 which is incorporated herein by reference, a semiconductordevice configured so that a buffer layer for buffering stress isinterposed between an Si substrate and a GaN semiconductor layer hasbeen disclosed. Although attention has been paid to several metalmaterials as materials for forming the buffer layer for buffering stressin the aforementioned Japanese Patent Publication No. Hei. 11-195814, Tihas been disclosed as one of the metal materials. That is, asemiconductor device configured so that a Ti layer is formed on an Sisubstrate and then a GaN semiconductor layer is formed on the Ti layerhas been disclosed.

It has been described more in detail in Japanese Patent Publication No.11-195814 that such a Ti layer is preferably used as an undercoat layerfor a GaN semiconductor layer when an Si substrate is used.

The inventors of the present application have further examined atechnique for laminating a Ti layer on an Si substrate and growing a GaNsemiconductor layer on the Ti layer as an undercoat layer. As a result,it has been found that both morphological characteristic andcrystallinity of a surface of the Ti layer are lowered when thesubstrate of Ti/Si is exposed to an environment of 700° C. or higher. Itis thought of that this is because Ti and Si react with each other atthe aforementioned temperature. Incidentally, there is a possibilitythat the reaction of Ti and Si has a bad influence on the crystallinityof the GaN semiconductor layer because the GaN semiconductor layer isgenerally grown at a temperature of about 1000° C.

This invention is designed to solve the problem found by the presentinventors and the configuration thereof is as follows.

That is, a GaN semiconductor device comprising:

a substrate of Si;

a Ti layer formed on the substrate;

a GaN semiconductor layer formed on the Ti layer; and

a heat-resisting layer which is interposed between the substrate and theTi layer to separate the substrate and the Ti layer from each other andwhich keeps the substrate and the Ti layer in a separate state at atemperature for the formation of the GaN semiconductor layer.

In the semiconductor device configured as described above according tothe present invention, the reaction of the Ti layer and the Si substrateis prevented securely because the heat-resisting layer is interposedbetween the Ti layer and the Si substrate. As a result, thecrystallinity of the GaN semiconductor layer is improved. The devicehaving the GaN semiconductor layer of good crystallinity fulfills apreferred operation. Incidentally, in the above description, both the Tilayer and the heat-resisting layer fulfill the role of an undercoatlayer.

(Si Substrate)

In the above description, the Si substrate preferably uses its (111)face so that the heat-resisting layer, etc. are grown on the (111) faceof the substrate successively.

(Heat-resisting Layer)

The heat-resisting layer is not particularly limited if the Si substrateand the Ti layer can be kept in a separate state at a temperature forthe formation of the GaN semiconductor layer. For example, silicide ofTi, Co, Ni, etc., a high-melting metal such as Ta, Mo, etc., or metalnitride such as TiN, ZrN, HfN, tantalum nitride, etc. can be used.

In the above description, the silicide is formed by means of forming afilm of each metal on the Si substrate and heating the Si substrate. Thehigh-melting metal or the metal nitride is formed by means of CVD(Chemical Vapor Deposition) such as plasma CVD, thermal CVD, lightenhanced CVD, MOCVD, etc., PVD (Physical Vapor Deposition) such assputtering, reactive sputtering, laser ablation, ion plating,evaporation, ECR, etc., or the like.

Also the thickness of the heat-resisting layer is not particularlylimited if the heat-resisting layer can prevent the respective materialsof the Si substrate and the Ti layer from reacting with each other. Forexample, the thickness of the heat-resisting layer is set to be in arange of from 50 to 10000 Å when TiN is used as the heat-resistinglayer.

The heat-resisting layer is preferably formed from an electricallyconductive material. Also the Si substrate and the Ti layer areelectrically conductive. As a result, electrodes can be formed onopposite faces of the semiconductor device, so that the “charge-up”problem can be solved.

When TiN is used as the heat-resisting layer, an Al layer or an Ag layeris preferably interposed between the Si substrate and the TiN layer. Thethickness of the Al or Ag layer is not particularly limited but may beset to be in a range of from 50 to 250 Å. For example, the Al or Aglayer is formed by means of evaporation or sputtering.

(Ti Layer)

Also the Ti layer is formed by the aforementioned means of CVD, PVD, orthe like. According to the inventors' examination, there is a risk thatthe peeling of the Ti layer occurs when the Ti layer is made thickerthan about 250 Å. Hence, the thickness of the Ti layer is preferably setto be not larger than 250 Å.

When the Ti layer is made thin, it is, however, a risk that the expectedbuffering function of the Ti layer cannot be fulfilled, that is, thefunction of buffering internal stress caused by the difference betweenthe thermal expansion coefficient of the Si substrate and the thermalexpansion coefficient of the GaN semiconductor cannot be fulfilled.

In this invention, therefore, heat-resisting layers and Ti layers (eachhaving a thickness of 250 Å or smaller) are laminated repetitively sothat the aforementioned buffering function is shared among the Tilayers. Hence, the buffering function of the Ti layers can be securedwhile the Ti layers are prevented from peeling off, so that the GaNsemiconductor layer can be prevented from cracking or being distorted.

The number of the repeated heat-resisting and Ti layers is notparticularly limited but, for example, set to be in a range of from 2 to10.

After the Ti layer is formed in the aforementioned manner, the Tilayer/heat-resisting layer/Si substrate is preferably heated. Thetemperature for the heating is in a range of from 600 to 1200° C.,preferably in a range of from 800 to 1200° C. The heating is performedin a vacuum or in an atmosphere of hydrogen.

A buffer layer is preferably interposed between the Ti layer and the GaNsemiconductor layer. The buffer layer is preferably formed ofAl_(a)Ga_(1−a)N (in which a is from 0.85 to 0.95), more preferablyformed of Al_(a)Ga_(1−a)N (in which a is about 0.9).

(GaN Semiconductor Layer)

The GaN semiconductor is a group III metal nitride semiconductor whichis generally represented by Al_(X)Ga_(Y)In_(1−X−Y)N (0≦X≦1, 0≦Y≦1,0≦X+Y≦1). The GaN semiconductor may further contain an optional dopant.

A method for forming such a GaN semiconductor layer is not particularlylimited but, for example, the GaN semiconductor layer is formed by aknown metal organic chemical vapor deposition method (hereinafterabbreviated as “MOCVD method”). Alternatively, the layer can be formedby a known molecular beam epitaxy method (MBE method).

As is commonly known, a light-emitting device or a photodetector isconfigured so that a light-emitting layer is sandwiched betweendifferent electrically conductive types of GaN semiconductor layers(clad layers). A double heterostructure, or the like, is applied to thelight-emitting layer. An electronic device represented by an FETstructure can be also formed from GaN semiconductors. In this manner, aplurality of GaN semiconductor layers formed on a Ti layer act on oneanother to fulfil a desired function.

Samples will be described below.

Sample 3

Layer Thickness TiN 3000 Å Al  100 Å Si substrate (111)  300 μm

An Al layer (thickness: about 100 Å) was evaporated onto a (111) face ofan Si substrate. Titanium nitride (thickness: about 3000 Å) was formedon the Al layer by a reactive sputtering method. The sample was heatedat 950° C. in a vacuum for 5 minutes. FIG. 13 shows a result of X-raydiffraction φ(PHI) scanning) of the sample. A quadraxial type singlecrystal diffraction meter (product name: X-pert) made by Philips Corp.was used as an X-ray diffraction instrument (the same meter is appliedalso to the following samples). See Journal of Electronic Materials,Vol. 25, No. 11, pp. 1740-1747, 1996, concerning φ(PHI) scanning. Inφ(PHI) scanning, peaks corresponding to crystal faces are obtained whenthe sample is rotated by 360 degrees. FIG. 13 shows peaks of TiN (200)face and TiN (220) face. It is thought of that the larger the value ofthe ordinate in FIG. 13 becomes, the better crystal is obtained. It isthought of that, when the crystallinity of TiN is good, thecrystallinity of a Ti layer grown on the TiN becomes good and,accordingly, the crystallinity of a GaN semiconductor layer becomesgood.

It is apparent from the result shown in FIG. 13 that the crystallinityof the TiN crystal produced in the aforementioned manner is good.

Sample 4

Layer Thickness TiN 3000 Å Ag  100 Å Si substrate (111)  300 μm

FIG. 14 shows a result of φ(PHI) scanning in the case where the Al layerin the sample 3 is replaced by an Ag layer (thickness: about 100 Å).Also in this case, a TiN layer good in crystallinity was obtained.

Sample 5

Layer Thickness Ti 15000 Å TiN  5000 Å Al  100 Å Si substrate (111)  300μm

FIG. 15 shows a result of φ(PHI) scanning in the case where Ti is grownon TiN (film thickness: about 5000 Å) in the sample 3 to evaluate thecrystallinity of Ti. Symmetric patterns of six peaks corresponding to Ti(102) face and Ti (112) face were confirmed, and a good single crystalTi layer was obtained.

Sample 6

Layer Thickness TiN 3000 Å Ti 1000 Å TiN  100 Å Al  100 Å Si substrate(111)  300 μm

In this sample, the thickness of a first TiN layer in the sample 3 wasset to be 100 Å and then a 1000 Å-thick Ti layer and a 3000 Å-thicksecond TiN layer were formed continuously by a reactive sputteringmethod.

FIG. 16 shows a result of φ(PHI) scanning to evaluate the crystallinityof the TiN layers. Also in this case, TiN layers good in crystallinitywere obtained.

Sample 7

Layer Thickness repetition of TiN (100 Å)/Ti (250 Å) (the number ofrepetitions: 10) TiN 3000 Å Al  100 Å Si substrate (111)  300 μm

In this sample, the thickness of a first TiN layer in the sample 3 wasset to be 3000 Å and then 250 Å-thick Ti layers and 100 Å-thick TiNlayers were formed alternately by 10 times. The TiN layers and the Tilayers were formed continuously by a reactive sputtering method.

Sample 8

Layer Thickness repetition of TiN (600 Å)/Ti (50 Å) (the number ofrepetitions: 4) TiN 600 Å Al 100 Å Si substrate (111) 300 μm

In this sample, the thickness of a first TiN layer in the sample 3 wasset to be 600 Å and then 50 Å-thick Ti layers and 600 Å-thick TiN layerswere formed alternately by 4 times. The TiN layers and the Ti layerswere formed continuously by a reactive sputtering method.

FIG. 17 shows a result of φ(PHI) scanning to evaluate the crystallinityof the TiN layers. Also in this case, TiN layers good in crystallinitywere obtained.

Sample 9

Layer Thickness Ti 15000 Å Al treated thermally  100 Å Si substrate(111)  300 μm

An Al layer (thickness: about 100 Å) was evaporated onto a (111) face ofan Si substrate at ordinary temperature. The substrate was heated at950° C. for 5 minutes in a vacuum environment. Then, a Ti layer(thickness: 15000 Å) was formed by means of sputtering.

FIG. 18 shows a result of φ(PHI) scanning to evaluate the crystallinityof the Ti layer (15000 Å). Also in this case, a Ti layer good incrystallinity was obtained.

Sample 10

Layer Thickness Ti 15000 Å Ti silicide   50 Å Si substrate (111)  300 μm

A Ti layer (thickness: about 50 Å) was evaporated onto a (111) face ofan Si substrate at ordinary temperature. The substrate was heated at950° C. for 5 minutes in a vacuum environment to make Ti react with Siaggressively to thereby form a Ti silicide layer. Then, a Ti layer(thickness: 15000 Å) was formed by means of sputtering.

Also in this case, six peaks corresponding to Ti (102) face and Ti (112)face were confirmed clearly. Hence, it was apparent that thecrystallinity of the Ti layer was good.

Sample 11

Layer Thickness Ti 15000 Å Co silicide  100 Å Si substrate (111)  300 μm

A Co layer (thickness: about 100 Å) was evaporated onto a (111) face ofan Si substrate at ordinary temperature. The substrate was heated at600° C. for 5 minutes in a vacuum environment to make Co react with Siaggressively to thereby form a Co silicide layer. Then, a Ti layer(thickness: 15000 Å) was formed by means of sputtering.

Also in this case, six peaks corresponding to Ti (102) face and Ti (112)face could be discriminated, so that the single crystal growth of the Tilayer was confirmed.

Sample 12

Layer Thickness Ti 15000 Å Ni silicide  100 Å Si substrate (111)  300 μm

An Ni layer (thickness: about 100 Å) was evaporated onto a (111) face ofan Si substrate at ordinary temperature. The substrate was heated at800° C. for 5 minutes in a vacuum environment to make Ni react with Siaggressively to thereby form an Ni silicide layer. Then, a Ti layer(thickness: 15000 Å) was formed by means of sputtering.

Also in this case, six peaks corresponding to Ti (102) face and Ti (112)face could be discriminated, so that the single crystal growth of the Tilayer was confirmed.

Sample 13

Layer Thickness TiN 10000 Å Al treated thermally  100 Å Si substrate(111)  300 μm

An Al layer (thickness: about 100 Å) was evaporated onto a (111) face ofan Si substrate at ordinary temperature. The substrate washeat-processed at 950° C. for 5 minutes in a vacuum environment. Then, aTiN layer (thickness: 10000 Å) was formed by means of sputtering.

FIG. 19 shows a result of φ(PHI) scanning to evaluate the crystallinityof the TiN layer (10000 Å). Peaks corresponding to TiN (200) face andTiN (220) face were confirmed. A TiN layer good in crystallinity wasobtained.

Sample 14

Layer Thickness TiN 10000 Å Ti silicide   50 Å Si substrate (111)  300μm

A Ti layer (thickness: about 50 Å) was evaporated onto a (111) face ofan Si substrate at ordinary temperature. The substrate was heated at950° C. for 5 minutes in a vacuum environment to make Ti react with Siaggressively to thereby form a Ti silicide layer. Then, a TiN layer(thickness: 10000 Å) was formed by means of sputtering.

When φ(PHI) scanning was observed to evaluate the crystallinity of theTiN layer (10000 Å), six peaks were confirmed clearly. Hence, it wasapparent that the TiN layer was grown as a single crystal.

Sample 15

Layer Thickness TiN 3000 Å sapphire substrate face a  300 μm

TiN (3000 Å) was formed on a face a of a sapphire substrate by areactive sputtering method. FIG. 20 shows a result of x-ray diffraction(φ(PHI) scanning) of the sample. It is apparent from the result shown inFIG. 20 that TiN of good crystallinity is formed also on the sapphiresubstrate. TiN of good crystallinity can be formed also on a face C ofthe sapphire substrate in the same manner as described above. Whenheating at 800° C. or higher is performed, the crystallinity of TiN isimproved more greatly. Ti can be further formed on the TiN and a GaNsemiconductor layer can be further formed on the Ti. A laminate ofTi/TiN may be repeated. In this case, the number of repetitions and therespective thicknesses of the layers are not particularly limited.

Sample 16

Layer Thickness TiN 3000 Å GaN  400 μm AlN buffer layer  160 Å sapphireface a  300 μm

TiN (3000 Å) was formed on GaN by a reactive sputtering method. FIG. 21shows a result of X-ray diffraction (φ(PHI) scanning). It is apparentfrom the result shown in FIG. 21 that TiN of good crystallinity isformed also on GaN.

Sample 17

Layer Thickness Ti 15000 Å TiN  3000 Å GaN  400 μm AlN buffer layer  160Å sapphire face a  300 μm

Ti was further grown on TiN in the sample 16 (before heating) by asputtering method. FIG. 22 shows a result of X-ray diffraction ((PHI)scanning). It is apparent from the result shown in FIG. 22 that thecrystallinity of the Ti layer formed on TiN/GaN is good.

Embodiments of this invention will be described below.

(Fifth Embodiment)

This embodiment shows a light-emitting diode 100. FIG. 23 shows theconfiguration of the light-emitting diode 100.

Specifications of respective layers are as follows.

Layer Composition Dopant (Thickness) p-type clad layer 18 p-GaN Mg (0.3μm) Light-emitting layer 17 Superlattice structure quantum well layerIn_(0.15)Ga_(0.85)N (35 Å) barrier layer GaN (35 Å) the number ofrepeated quantum well and barrier layers: 1 to 10 n-type clad layer 16n-GaN Si (4 μm) Buffer layer 15 Al_(0.9)Ga_(0.1)N (150 Å) Ti layer 13 Ticrystal (250 Å) TiN layer 14 TiN crystal (3000 Å) Al layer 12 Al (100 Å)Substrate 11 Si (111)  (300 μm)

The n-type clad layer 16 may be of a double-layered structure with an n⁻layer of a low electron density on the light-emitting layer 17 side andan n⁺ layer of a high electron density on the buffer layer 15 side.

The light-emitting layer 17 is not limited to the superlattice structurebut a single hetero type, a double hetero type, a homo-junction type, orthe like, can be used as this layer.

An Al_(X)In_(Y)Ga_(1−Y−X)N (inclusive of X=0, Y=0, X=Y=0) layer, whichhas a wide band gap and which is doped with an acceptor such asmagnesium, or the like, may be interposed between the light-emittinglayer 17 and the p-type clad layer 18. This technique is employed forpreventing electrons implanted into the light-emitting layer 17 frombeing diffused into the p-type clad layer 18.

The p-type clad layer 18 may be of a double-layered structure with a p⁻layer of a low hole density on the light-emitting layer 17 side and a p⁺layer of a high hole density on the electrode side.

In the light-emitting diode 100 shown in this embodiment, thelight-emitting structure of the Ti layer 13 and above is a knownstructure. Hence, a known method can be also employed as a method forforming the structure.

Detailed description will be made below.

The Al layer 12 formed on the Si (111) face is grown by a generalevaporation method.

The TiN layer 14 and the Ti layer 13 are formed by a general reactivesputtering method.

Then, the Ti/TiN/Al/Si sample is transferred from a sputtering apparatusinto a chamber of an MOCVD apparatus. The chamber is evacuated (to2×10⁻³ Pa). In this state, the sample is heated to 650° C. and kept at650° C. for 5 minutes.

Then, the buffer layer 15 of AlGaN is grown at a growth temperature of350° C. In the condition that the temperature is further raised to 1000°C., the n-type clad layer 16 and layers following the n-type clad layer16 are formed in accordance with an ordinary method (MOCVD method). Inthis growth method, an ammonia gas and gasses of group III metal alkylcompounds such as trimethylgallium (TMG), trimethylaluminum (TMA), andtrimethylindium (TMI) are supplied to a substrate that has been heatedto an appropriate temperature and are subjected to a thermaldecomposition reaction to thereby grow a desired crystal on thesubstrate.

The crystallinity of the GaN semiconductor layer formed in thisembodiment in the aforementioned manner is good.

A light-transmissible electrode 19, which is constituted by a thin filmcontaining gold, is laminated to cover the substantially almost wholearea of an upper face of the p-type clad layer 18. Ap-type electrode 20,which is constituted also by a material containing gold, is formed onthe light-transmissible electrode 19 by means of evaporation.

An n-type electrode 30 is formed on the substrate 11. A wire is bondedto a desired position. A light-emitting device made by this process haslight intensity of 1 cd at 470 nm.

(Sixth Embodiment)

FIG. 24 shows a semiconductor device as a sixth embodiment of thisinvention. The semiconductor device shown in this embodiment is alight-emitting diode 200. Incidentally, the same parts as shown in FIG.23 are referred to by the same characters so that the descriptionthereof will be omitted.

Specifications of respective layers are as follows.

Layer Composition Dopant (Thickness) n-type clad layer 28 n-GaN Si (0.3μm) light-emitting layer 17 Superlattice structure quantum well layerIn_(0.15)Ga_(0.85)N (35 Å) barrier layer GaN (35 Å) the number ofrepeated quantum well and barrier layers: 1 to 10 p-type clad layer 26p-GaN Mg (4 μm) buffer layer 15 Al_(0.9)Ga_(0.1)N (150 Å) Ti layer 13bTi crystal (250 Å) TiN layer 14b TiN crystal (100 Å) Ti layer 13a Ticrystal (250 Å) TiN layer 14a TiN crystal (100 Å) Al layer 12 Al (100 Å)substrate 11 Si (111) (300 μm)

As described above, in this embodiment, laminates of Ti/TiN are formedrepetitively. The number of repeated Ti/TiN laminates is notparticularly limited. Also the thicknesses of the respective layers arenot particularly limited but the thickness of each of the Ti layers ispreferably set to be not larger than 250 Å from the point of view ofsecurely preventing the layer from peeling.

The same producing method as in the fifth embodiment is applied to thisembodiment.

In this embodiment, the p-type clad layer 26, the light-emitting layer17 and the n-type clad layer 28 are grown successively on the bufferlayer 15 to thereby form the light-emitting diode 200. In the case ofthe device 200, the light-transmissible electrode (see the referencecharacter 19 in FIG. 23) can be omitted because the n-type clad layer 28of low resistance forms the uppermost face.

In FIG. 24, the reference character 30 designates an n-type electrodeformed on the Si substrate 11. The light-emitting device made by thisprocess has a light intensity of about 1.2 cd at 470 nm.

The device to which the present invention is applied is not limited tothe aforementioned light-emitting diode. For example, the preventinvention may be applied to optical devices such as a photodetector, alaser diode, etc. and also to electronic devices such as an FETstructure, etc.

The prevent invention may be further applied to laminates which areintermediates of these devices.

This invention is not limited to the aforementioned description of themode for carrying out the invention and the embodiments thereof at all,and includes various modifications that can be conceived by thoseskilled in the art without departing from the scope of claim for apatent.

The following items will be disclosed below.

-   (140) A laminate comprising:

a substrate made of Si;

a Ti layer formed on the substrate;

a GaN semiconductor layer formed on the Ti layer; and

a heat-resisting layer interposed between the substrate and the Ti layerto separate the substrate and the Ti layer from each other so that thesubstrate and the Ti layer are kept in a separate state at a temperaturefor the formation of the GaN semiconductor layer.

-   (141) A laminate according to the paragraph (140), wherein the    heat-resisting layer is formed of any one of silicide, high-meting    metal and metal nitride.-   (142) A laminate according to the paragraph (141), wherein: the    silicide is one member selected from the group consisting of Ti    silicide, Co silicide, and Ni silicide; thermally treated Al; the    high-meting metal is either Ta or Mo; and the metal nitride is one    member selected from the group consisting of TiN, ZrN, HfN, and    tantalum nitride.-   (143) A laminate according to any one of the paragraphs (140) to    (142), wherein the heat-resisting layer is formed on a (111) face of    the substrate.-   (144) A laminate according to any one of the paragraphs (140) to    (143), wherein the Ti layer and the heat-resisting layer are    laminated repetitively.-   (145) A laminate according to the paragraph (144), wherein the    thickness of each of the Ti layers is in a range of from 10 to 250    Å.-   (146) A laminate comprising:

a substrate;

a layer formed on the substrate and constituted by repetition of acombination of a Ti layer and a heat-resisting layer; and

a GaN semiconductor layer formed on the repetition layer, wherein

the heat-resisting layer has a melting point substantially higher thanthe temperature for the formation of the GaN semiconductor layer.

-   (147) A laminate according to the paragraph (147), wherein the    thickness of each of the Ti layers is in a range of from 10 to 250    Å.

The inventors have made further examination eagerly. As a result, thefollowing invention has been conceived.

A group III nitride compound semiconductor device comprising:

a substrate;

an undercoat layer of electrically conductive metal nitride formed onthe substrate; and

a group III nitride compound semiconductor layer formed on the undercoatlayer, wherein

an electrode is provided on the undercoat layer.

According to the group III nitride compound semiconductor deviceconfigured as described above, not only the group III nitride compoundsemiconductor layer is formed on the undercoat layer made electricallyconductive but also the electrode is provided on the undercoat layer.Hence, there is no necessity of providing a thick portion and a thinportion in the n-type layer as required in the background art. Hence,there is no concentration of current in the boundary between the thickand thin portions, so that the operating voltage of the device can bereduced.

In the above description, the material of the substrate is notparticularly limited if the substrate is adapted to the group IIInitride compound semiconductor. Sapphire, silicon, silicon carbide, zincoxide, gallium phosphide, gallium arsenide, magnesium oxide, manganeseoxide, etc. can be taken as examples of the material of the substrate.

This invention is particularly useful for electrically insulatingsubstrates of sapphire, zinc oxide, etc.

Titanium nitride, hafnium nitride, zirconium nitride or tantalum nitrideis selected as the electrically conductive metal nitride. The method forgrowing these metal nitrides on the substrate is not particularlylimited but CVD (Chemical Vapor Deposition) such as MOCVD, plasma CVD,thermal CVD, optical CVD, etc., PVD (Physical Vapor Deposition) such assputtering, reactive sputtering, laser ablation, ion plating,evaporation, ECR, etc., or the like, may be used as this method.

The thickness of the undercoat layer is preferably set to be in a rangeof from 0.3 to 10 μm. The reason why the thickness of the undercoatlayer is set to be not smaller than 0.3 μm is that the undercoat layeris kept thick sufficiently to form the electrode on the undercoat layereven in the case where etching has influence on the undercoat layer whenthe group III nitride compound semiconductor layer is etched to revealthe undercoat layer. The reason why the thickness of the undercoat layeris set to be not larger than 10 μm is wholly an economic reason.

Another layer may be interposed between the undercoat layer and thesubstrate. According to the inventors' examination, titanium nitride isgrown on a (111) face of silicon used as a substrate in the condition ofa film-forming temperature of 500° C. or higher. When an Al layer isinterposed between the (111) face and the titanium nitride layer, asingle crystal film of titanium nitride can be formed even at a lowtemperature of about 300° C. The thickness of the Al layer is notparticularly limited but is set to be about 100 Å. Also the method forforming the Al layer is not particularly limited but, for example, theAl layer may be formed by means of evaporation or sputtering, and so on.

After the undercoat layer is formed on the substrate, the substrate ispreferably heated. The heating condition is a temperature of from 600 to1200° C. (more preferably from 800 to 1200° C.) in a hydrogen gas or ina vacuum (more preferably in a hydrogen gas).

The group III nitride compound semiconductor is represented by thegeneral formula Al_(X)Ga_(Y)In_(1−X−Y)N (0≦X≦1, 0≦Y≦1, 0≦X+Y≦1), whichmay further contain group III elements such as boron (B) and thallium(Tl) and in which the nitrogen (N) may be partially replaced byphosphorus (P), arsenic (As), antimony (Sb) or bismuth (Bi). The groupIII nitride compound semiconductor may contain an optional dopant.

The method for forming the group III nitride compound semiconductorlayer is not particularly limited but, for example, this layer may beformed by a known metal organic chemical vapor deposition method.Alternatively, this layer may be formed by a known MBE method.

Another group III nitride compound semiconductor layer having a latticeconstant substantially intermediate between the lattice constant ofmetal nitride constituting the undercoat layer and the lattice constantof the group III nitride compound semiconductor layer (generallyrepresented by a GaN layer) constituting the device structure ispreferably interposed as a buffer layer between the undercoat layer andthe group III nitride compound semiconductor layer. This is for thepurpose of relaxing the stress for lattice mismatch between theundercoat layer and the group III nitride compound semiconductor layerconstituting the device structure.

When titanium nitride is selected as the undercoat layer to form a GaNclad layer of a light-emitting device on the undercoat layer, an AlNlayer (about 150 Å) is preferably formed as a buffer layer on thetitanium nitride layer. As a forming method, the undercoat layer isheated (1000° C., 5 minutes) in an atmosphere of hydrogen and then thegroup III nitride compound semiconductor layer is grown at about 1000°C. by an MOCVD method. Alternatively, the group III nitride compoundsemiconductor layer is grown on the undercoat layer of titanium nitrideby a sputtering method without heating.

Preferably, AlN to be used as a buffer layer is doped with Si, or thelike, to be provided as an n-type semiconductor.

After the group III nitride compound semiconductor layer is laminated, apredetermined portion of the layer is removed by means of etching sothat the undercoat layer is revealed.

Alternatively, a predetermined portion of the undercoat layer may becovered with a mask in advance to prevent the group III nitride compoundsemiconductor layer from being grown on the portion of the undercoatlayer so that the undercoat layer can be revealed by means of peelingthe mask. Silicon oxide or silicon nitride is used as the material ofthe mask.

The position and shape of the revealed portion of the undercoat layerare not particularly limited but a circumferential edge portion of theundercoat layer is preferred from the point of view of the fact that theelectrode must be formed thereon. When the shape of the device is squarein plan view, that is, a corner portion of the undercoat layer ispreferably revealed.

The material of the electrode connected to the undercoat layer is notparticularly limited if ohmic contact can be obtained between theundercoat layer and the electrode. Taking wire-bonding into account, anAl, Au, an Au alloy, or the like, can be used as the material of theelectrode.

A seventh embodiment of this invention will be described below withreference to the drawings.

A light-emitting diode 10 shown in FIG. 25 will be taken as an exampleof the device.

Specifications of respective layers are as follows.

Layer Composition Dopant (Thickness) p-type clad layer 18 p-GaN Mg (0.3μm) Light-emitting layer 17 Superlattice structure quantum well layerIn_(0.15)Ga_(0.85)N (35 Å) barrier layer GaN (35 Å) the number ofrepeated quantum well and barrier layers: 1 to 10 n-type clad layer 16n-GaN Si (4 μm) buffer layer 15 n-AlN Si (150 Å) TiN layer 14 TiN single(3000 Å) (undercoat layer) crystal substrate 11 Sapphire (300 μm)

In the above description, the buffer layer 15 is doped with an n-typedopant such as silicon, or the like, in order to secure the electricallyconductive characteristic of the buffer layer 15.

The n-type clad layer 16 may be of a double-layered structure with an n⁻layer of a low electron density on the light-emitting layer 17 side andan n⁺ layer of a high electron density on the buffer layer 15 side.

The light-emitting layer 17 is not limited to the superlattice structurebut a single hetero type, a double hetero type, a homo-junction type, orthe like, can be used as this layer.

An Al_(X)Ga_(Y)In_(1−X−Y)N (0≦X≦1, 0≦Y≦1, 0≦X+Y≦1) layer, which has awide band gap and which is doped with an acceptor such as magnesium, orthe like, may be interposed between the light-emitting layer 17 and thep-type clad layer 18. This technique is employed for preventingelectrons implanted into the light-emitting layer 17 from being diffusedinto the p-type clad layer 18.

The p-type clad layer 18 may be of a double-layered structure with a p⁻layer of a low hole density on the light-emitting layer 17 side and a p⁺layer of a high hole density on the electrode side.

The TiN layer is formed by a general reactive sputtering method.

Then, the TiN/sapphire sample is transferred from a sputtering apparatusinto a chamber of an MOCVD apparatus. While a hydrogen gas is made toflow into the chamber, the sample is heated to 1000° C. and kept at1000° C. for 5 minutes.

Then, the buffer layer 15 of AlN is grown at a growth temperature of1000° C. In the condition that the temperature is kept 1000° C., then-type clad layer 16 and layers following the n-type clad layer 16 areformed in accordance with an ordinary method (MOCVD method). In thisgrowth method, an ammonia gas and gasses of group III metal alkylcompounds such as trimethylgallium (TMG), trimethylaluminum (TMA), andtrimethylindium (TMI) are supplied to a substrate that has been heatedto an appropriate temperature and are subjected to a thermaldecomposition reaction to thereby grow a desired crystal on thesubstrate.

Alternately, the respective group III nitride compound semiconductorlayers may be formed by an MBE method.

After the respective group III nitride compound semiconductor layers areformed, the undercoat layer 14 of titanium nitride is revealed by meansof etching.

Then, a light-transmissible electrode 19 is formed on the substantiallywhole face of the p-type clad layer 18 by means of evaporation. Thelight-transmissible electrode 19 is constituted by a thin filmcontaining gold. A p-type electrode 20, which is constituted also by amaterial containing gold, is formed on the light-transmissible electrode19 by means of evaporation.

Further, an n-type electrode 21 of an Au alloy is formed on the revealedportion of the undercoat layer 14 by means of evaporation.

According to the light-emitting diode configured as described above, the“current concentration” problem in the background art is solved becausethe n-type layer has a metallic conductivity. Further, metal nitridetouching the electrodes is more excellent in terms of electricconduction than semiconductor. Hence, a low operating voltage can beachieved.

Further, metal nitride represented by titanium nitride generally has ametallic color. Hence, there is also an effect that light generated inthe light-emitting layer toward the substrate is reflected by the metalnitride efficiently to thereby improve the brightness of thelight-emitting diode.

Further, metal nitride represented by titanium nitride is generally highin heat conductivity. Hence, heat can be radiated efficiently from therevealed portion of the undercoat layer.

The group III nitride compound semiconductor layer formed on theundercoat layer may be provided as a p-type layer whereas the othergroup III nitride compound semiconductor layer, which is the uppermostlayer, may be provided as an n-type layer. In this case, thelight-transmissible electrode (seethe reference character 19 in FIG. 25)can be omitted.

The device to which the present invention is applied is not limited tothe aforementioned light-emitting diode. The present invention may beapplied also to optical devices such as a light-receiving diode, a laserdiode, a solar cell, etc., bipolar devices such as a rectifier, athyristor, a transistor, etc., unipolar devices such as an FET, etc.,and electronic devices such as a microwave device, etc.

The present invention may be further applied to laminates which areintermediates of these devices.

This invention is not limited to the aforementioned description of themode for carrying out the invention and embodiments thereof at all, andincludes various modifications that can be conceived by those skilled inthe art without departing from the scope of claim for a patent.

The following items will be disclosed.

-   (150) A laminate comprising:

a substrate;

an undercoat layer of electrically conductive metal nitride formed onthe substrate; and

a group III nitride compound semiconductor layer formed on a face of theundercoat layer, wherein

the undercoat layer has a region which is a part of the face of theundercoat layer for the formation of the group III nitride compoundsemiconductor layer and which is not covered with the group III nitridecompound semiconductor layer.

-   (151) A laminate according to the paragraph (150), wherein the metal    nitride is constituted by at least one member selected from the    group consisting of titanium nitride, zirconium nitride, hafnium    nitride, and tantalum nitride.-   (152) A laminate according to the paragraph (150) or (151), wherein:    the shape of the device is square in plan view; and a portion put    between two sides forming a corner portion of the square is the    region which is not covered with the group III nitride compound    semiconductor layer.-   (153) A laminate according to any one of the paragraphs (150) to    (152), wherein the region which is not covered with the group III    nitride compound semiconductor layer is exposed.-   (154) A method of producing a group III nitride compound    semiconductor device, comprising the steps of:

forming an undercoat layer of electrically conductive metal nitride on asubstrate;

forming a group III nitride compound semiconductor layer on theundercoat layer;

removing the group III nitride compound semiconductor layer partially toreveal a part of the undercoat layer; and

connecting an electrode to the revealed part of the undercoat layer.

-   (155) A producing method according to the paragraph (154), wherein    the metal nitride is constituted by at least one member selected    from the group consisting of titanium nitride, zirconium nitride,    hafnium nitride, and tantalum nitride.-   (156) A producing method according to the paragraph (154) or (155),    wherein: the shape of device is square in plan view; the group III    nitride compound semiconductor layer is formed on the whole area of    the square device; and the group III nitride compound semiconductor    layer is etched to reveal a corner portion of the right-angled    quadrilateral to thereby reveal the corner portion of the undercoat    layer.-   (157) A method of producing a laminate, comprising the steps of:

forming an undercoat layer of electrically conductive metal nitride on asubstrate;

forming a group III nitride compound semiconductor layer on theundercoat layer; and

removing the group III nitride compound semiconductor layer partially toreveal a part of the undercoat layer.

-   (158) A producing method according to the paragraph (157), wherein    the metal nitride is constituted by at least one member selected    from the group consisting of titanium nitride, zirconium nitride,    hafnium nitride, and tantalum nitride.-   (159) A producing method according to the paragraph (157) or (158),    wherein: the shape of the device is square in plan view; the group    III nitride compound semiconductor layer is formed on the whole area    of square device; and the group III nitride compound semiconductor    layer is etched to reveal a corner portion of the right-angled    quadrilateral to thereby reveal the corner portion of the undercoat    layer.

1. A semiconductor device comprising: a substrate; an undercoat layerformed on said substrate and comprising a metal nitride; and a group IIInitride compound semiconductor layer formed on said undercoat layer, andseparated from said substrate by at least said undercoat layer, whereinsaid metal nitride comprises at least one of Nb, V, Y, and Cr.
 2. Asemiconductor device according to claim 1, wherein said metal nitridedirectly contacts said group III nitride compound semiconductor layer.3. A semiconductor device according to claim 1, wherein said substratecomprises one member selected from the group consisting of sapphire,silicon carbide, gallium nitride, silicon, gallium phosphide, andgallium arsenide.
 4. A semiconductor device according to claim 1,wherein said substrate comprises a cubic crystal material comprising a(111) face on which said undercoat layer is formed.
 5. A semiconductordevice according to claim 1, further comprising: a first electrodeprovided on said undercoat layer.
 6. A semiconductor device according toclaim 1, wherein said undercoat layer is selected for providing apredetermined crystallinity of said group III nitride compoundsemiconductor layer.
 7. A semiconductor device according to claim 1,wherein said undercoat layer has a thickness in a range of 0.1 to 10 μm.8. A semiconductor device according to claim 1, further comprising: ametal layer adjacent to said undercoat layer.
 9. A semiconductor deviceaccording to claim 1, wherein said group III nitride compoundsemiconductor layer comprises a light-emitting layer.
 10. Asemiconductor device according to claim 9, wherein said undercoat layerreflects light emitted from said light-emitting layer.
 11. Asemiconductor device according to claim 1, wherein said undercoat layercomprises a continuously-formed undercoat layer.